CMake: Disable test programs when compiling with Visual Studio
CMake: Disable test programs when compiling with Visual Studio

The test programs will build fine when compiled under MinGW but won't
compile under Visual Studio. So we disable them for now and will
re-enable them once they are fixed.

Signed-off-by: Paul Cercueil <73d292422978d45c9eeef455bb1b24a0db453722@analog.com>

Sunderfield/libiio,analogdevicesinc/libiio,gburca/libiio,sensarliar/libiio,sensarliar/libiio,analogdevicesinc/libiio,gburca/libiio,analogdevicesinc/libiio,Sunderfield/libiio,Sunderfield/libiio,sensarliar/libiio,analogdevicesinc/libiio,gburca/libiio